Error rate of multi-level rapid prototyping trajectories for pedicle screw placement in lumbar and sacral spine

Free-hand pedicle screw placement has a high incidence of pedicle perforation which can be reduced with fluoroscopy, navigation or an alternative rapid prototyping drill guide template. In our study the error rate of multi-level templates for pedicle screw placement in lumbar and sacral regions was evaluated.

A case series study was performed on 11 patients. Seventy-two screws were implanted using multi-level drill guide templates manufactured with selective laser sintering. According to the optimal screw direction preoperatively defined, an analysis of screw misplacement was performed. Displacement, deviation and screw length difference were measured. The learning curve was also estimated.

Twelve screws (17%) were placed more than 3.125 mm out of its optimal position in the centre of pedicle. The tip of the 16 screws (22%) was misplaced more than 6.25 mm out of the predicted optimal position. According to our predefined goal, 19 screws (26%) were implanted inaccurately. In 10 cases the screw length was selected incorrectly: 1 (1%) screw was too long and 9 (13%) were too short. No clinical signs of neurovascular lesion were observed. Learning curve was insignificantly noticeable (P=0.129).

In our study, the procedure of manufacturing and applying multi-level drill guide templates has a 26% chance of screw misplacement. However, that rate does not coincide with pedicle perforation incidence and neurovascular injury. These facts along with a comparison to compatible studies make it possible to summarize that multi-level templates are satisfactorily accurate and allow precise screw placement with a clinically irrelevant mistake factor. Therefore templates could potentially represent a useful tool for routine pedicle screw placement.